Smooth base stock composed of nonstandard fibers

ABSTRACT

A smooth base stock useful in various applications, but particularly useful in high quality imaging, comprising nonstandard fibers is disclosed. The base stock fibers have a fiber length weighted average of greater than about 0.9 mm and the base stock has a roughness of less than about 2.0 micron Ra.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/479,119, filed Jun. 17, 2003, which is related to U.S. ProvisionalApplication No. 60/479,118, entitled “BINDER SELECTION FOR COATEDPHOTOGRAPHIC BASE STOCK” and U.S. Provisional Application No.60/478,991, entitled “PIGMENT SELECTION FOR COATED PHOTOGRAPHIC BASESTOCK.” The disclosures of these provisional applications are herebyincorporated by reference.

This application is related to contemporaneously filed U.S. applicationSer. No. ______, entitled “BINDER SELECTION FOR COATED PHOTOGRAPHIC BASESTOCK” and U.S. application Ser. No. ______, entitled “PIGMENT SELECTIONFOR COATED PHOTOGRAPHIC BASE STOCK.” The disclosures of theseapplications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to smooth base stock for high qualityimaging, and, more particularly, to smooth base stock composed ofnonstandard fibers.

Obtaining photo quality prints by conventional silver halidephotography, ink jet printing, dye sublimation, thermal dye transfer, orother like methods is dependent upon the smoothness of the base stockforming the base material for such printing papers. The base stock istypically comprised of cellulose fibers, upon the top and/or bottom sideof which polyolefin or polyester films may be extruded or laminated. Animaging coating is applied on top of the poly film on one or both sides.Examples of imaging coatings include photosensitive emulsions, water orpigment-based ink receptive layers, thermal dye-recording layers, orother specialty coatings appropriate for a given imaging method. Thesmoothness of the base stock determines the appearance and surfaceuniformity of the final image.

It is known that the addition of mineral pigments to a raw stock inplace of fiber can improve surface smoothness. Doing so however, cancreate problems when the basis weight, caliper, and stiffness propertiesof the base stock are specified. Too much filler pigment can result in adecrease in caliper and stiffness for a desired basis weight andsmoothness.

Being able to achieve high levels of smoothness in a paper base stock isprimarily influenced by the cellulose fiber properties, the uniformityof fiber distribution comprising the base stock (formation), and thecalendering or densification processes of the base stock. Fibers can bethought of as hollow tubes with a characteristic length and cell wallthickness.

It is well known that formation (uniformity of fiber distribution withina paper base stock), fiber length and fiber wall thickness contribute tosmoothness. The more uniform the fiber distribution, the betterformation, and the less chance of high and low areas occurring on thesurface of paper causing a rough surface. Softwood fibers aresignificantly longer than hardwood fibers; therefore, hardwood fibersare preferred when smoothness is a desired property. Shorter fibers alsocontribute to better formation due to a lower tendency to flocculate andby their ability to pack together more tightly. Fiber cell wallthickness will influence the compressibility or ability of fibers toflatten during drying and when compressed during densification. Fiberswith thick cell walls are stiffer and resist collapse whereas fiberswith thin cell walls are easily compressed and produce a dense,well-formed base stock. Hardwood fibers with a thin cell wall alsoprovide more fibers per gram, further contributing to formation andsmoothness. To optimize the benefits that fiber characteristicscontribute to a smooth base stock, base stocks used for photographicquality papers typically are comprised of fibers that are short and/orhave thin fiber cell walls.

Accordingly, conventional techniques for providing a uniform base sheethaving the desired smoothness utilize short fibers. In accordance withthese conventional methods, the desired fiber length-weighted average,as measured by a Kajaani fiber analyzer, has been described to bebetween 0.4 to 0.58 mm (U.S. Pat. Nos. 6,391,532, 6,364,997, and6,107,014), equal to or less than 0.5 mm (U.S. Pat. Nos. 5,250,496 and5,288,690) or a length between 0.4 to 0.9 mm (JP-A-61-69649).

SUMMARY OF THE INVENTION

The present invention provides a smooth base stock for high qualityimaging. The base stock is characterized in that it utilizes nonstandardfibers yet provides the smoothness and other physical propertiesrequired for high quality imaging. In accordance with certainembodiments, the base stock of the present invention comprises fibershaving a length weighted average of greater than 0.9 mm and the basestock has a roughness of from about 1.2 micron Ra to about 1.5 micronRa.

In accordance with another embodiment of the present invention, the basestock is composed of fibers having a population below about 10×10⁶fibers per gram. According to certain aspects of the invention, the basestock in accordance with the present invention exhibits the desiredsmoothness and yet is substantially free of filler pigments.

In accordance with another aspect of the invention, a method forproducing a base stock for use in forming a recording material isdisclosed. The method includes the steps of providing a fiber slurrycomposed of fibers having a length weighted average fiber length aboveabout 1 mm, forming a web of the fibers and subjecting the web to asmoothing operation to provide a base stock having a roughness of fromabout 1.2 micron Ra to about 1.5 micron Ra. The method may also includea refining step wherein the fibers, after the refinement treatment, havea length-weighted average fiber length of above about 0.9 mm.

In accordance with another aspect of the invention, a support materialfor an image forming system is provided. The support material includes abase stock composed of fibers having a length weighted average ofgreater than about 0.9 mm and a roughness of from about 1.2 micron Ra toabout 1.5 micron Ra and an image forming or image receptive coatinglayer on at least one side of the base stock wherein the image formingor image receptive coating is selected from the group consisting of aphotosensitive emulsion, an ink jet receptive coating, a thermal dyerecording layer and a pigment based ink receptive layer.

In accordance with specific embodiments of the invention, the supportmaterial further comprises a polyolefin or polyester coating layerdisposed between the base stock and the image forming or image receptivecoating layer on one or both sides of the support material.

DETAILED DESCRIPTION

In describing the preferred embodiment, certain terminology will beutilized for the sake of clarity. It is intended that such terminologyinclude not only the recited embodiments but all technical equivalentswhich operate in a similar manner, for a similar purpose, to achieve asimilar result. All documents cited are, in relevant part, incorporatedherein by reference; the citation of any document is not to be construedas an admission that it is prior art with respect to the presentinvention.

The term “nonstandard fibers” refers to fibers that are not typicallyused for producing smooth, photo-quality papers. More specifically,nonstandard fibers are those having an unrefined average fiber length ofgreater than about 1.0 mm.

The term “average fiber length,” refers to the length weighted averagefiber length as determined with a suitable fiber length analysisinstrument such as a Kajaani Model FS-200 fiber analyzer.

The term “population” refers to the number of fibers per gram.

The base stock of the present invention may be used in any image formingsystem in which a smooth base sheet is required to provide a highquality image. By way of example, it may be used in conjunction withphotosensitive emulsions, water or pigment-based ink receptive layers,thermal dye-recording layers, or other specialty coatings appropriatefor a given imaging method.

Base stock for papers that produce high quality images requireexceptionally smooth surfaces. Fiber used in the manufacture of thesepapers is generally natural cellulose fiber, but synthetic fiber mayalso be used. The base stock can be produced on a Fourdrinier orcylinder paper machine. Achieving the desired level of smoothness isdependent on fiber characteristics, fiber treatment, and method of basestock densification.

The base stock of the present invention can include various additives astypically used in producing base stocks. During manufacture of the basestock, chemicals may be added to impart water resistance, wet or drystrength, and to achieve color and brightness targets, depending uponthe final product application. For example, sizing agents, dry and wetstrengthening agents, fillers, pH adjusters, pigments, dyes andfluorescent brighteners may be added. The additives and amounts neededto obtain a base stock having the desired properties are known to thoseskilled in the art.

Fiber content analysis of a conventional photographic base stock gavethe following wood species results: 34% eucalyptus, 24% maple, 23%aspen, 12% birch, 5% beech, and 2% ash. Unrefined fiber lengths of thesespecies are presented. The Eucalyptus family provides the shortesthardwood fiber available with an average fiber length as low as 0.65 mm.Maple is about 0.9 mm and aspen is about 1.0 mm. Other hardwood fiberspecies are greater than 1.0 mm in length. Cell wall thickness ofeucalyptus, maple, aspen, and birch is in the range of 3 to 4micrometers.

Fiber content analysis for a base stock sample in accordance with aspecific embodiment of the present invention gave the following woodspecies: 72% oak, 10% yellow poplar, 9% gum, 4% maple, the remainderbeing small amounts of other various hardwood species. Analysis of othersamples of base stock in accordance with this aspect of the inventiongave results that varied somewhat for percentages of species fiberspresent, but the predominant specie in all samples was oak, and the fourspecies listed above comprised no less than 83% and generally more than90% of the fiber in accordance with these embodiments of the invention.Unrefined fiber lengths are: oak is 1.25 mm, yellow poplar is 1.9 mm,and gum is 1.85 mm. Averaged fiber cell wall thickness for oak, yellowpoplar, and gum is approximately 6.0 microns. Accordingly, the fibercomposition of the invention base stock is significantly different fromthe fiber composition described in the prior art as being essential forproducing a smooth base stock necessary for photo quality images. Basedon the teachings in the prior art, one of skill in the art looking toproduce a base stock for photo-quality images would use short fibers andexpect better results with shorter fibers. By contrast, the presentinvention is directed to a base stock exhibiting the desired smoothnesseven though the fibers used are relatively long and typically consideredas unsuitable for photo-quality paper. The ability to use longer fibersis advantageous from a cost perspective as the longer fibers typicallyare less expensive than the short fibers used with conventionalphoto-quality papers.

Base stock in accordance with certain aspects of the present inventionincludes at least 50% nonstandard fibers, more particularly at least 80%nonstandard fibers and in certain embodiments at least 90% nonstandardfibers based on the total fiber content.

Fiber population, or fibers per gram, is another measure of fiberproperties indicative of the differences between fibers used inconventional base stocks for high image quality imaging and the fibersused in the present invention. The population of conventional fiberstypically is greater than about 10×10⁶ fibers per gram. By contrast, thepopulation for the majority of fibers used in the base stock of thepresent invention is less than about 10×10⁶ fibers per gram, typicallyless than about 7×10⁶ fibers per gram. Base stock in accordance withcertain aspects of the present invention includes at least 50% fibershaving a population less than about 10×10⁶ fibers per gram and moreparticularly at least 80% fibers having a population less than about10×10⁶ fibers per gram based on the total fiber content.

In a conventional paper making process, a number of steps are requiredto make a base stock. For the purposes of certain embodiments of thisinvention, one important step relates to the refining process. Thefibers are refined prior to being pumped to the paper machine head boxand formed into a paper web. During the refining step, fibers that havebeen previously treated in the pulping and bleaching stages are passedthrough refiners where the fibers experience a high degree of shear tofurther change the characteristics of the fiber. Refining can alter thecharacteristics of the fiber by increasing fiber surface area byfillibrating and by reducing fiber length. In some cases, speciallydesigned refiners are used to reduce fiber length by employing a cuttingaction. In accordance with conventional paper making processes forproducing base stock for high quality images, the refining treatmenttypically includes a combination of two refining methods. The first stepis disc refining which will fillibrate the fiber and cause somereduction in fiber length. The second refining step utilizes a conicalrefiner or mixer to shorten or cut fibers as described in U.S. Pat. No.6,107,014. Using a fiber mixture described previously, the resultingconventional fiber mix has a preferred fiber length-weighted averagebetween 0.4 and 0.58 mm. References in the prior art for the manufactureof base stock for high quality images refer to a fiber length-weightedaverage equal to or less than 0.5 mm (U.S. Pat. Nos. 5,250,496 and5,288,690). With the base stock of the present invention, the cuttingrefining step may be eliminated. The refining treatment in accordancewith certain aspects of the present invention results in base stockcomposed of a fiber mixture having a length-weighted average greaterthan about 0.9 mm. The ability to provide a base stock having thedesired smoothness while eliminating a refining step typically utilizedin the prior art is another advantage obtained in accordance withcertain aspects of the present invention.

The basis weight of the raw base paper will typically be from about 50to about 250 g/m², more particularly from about 100 to about 200 g/m².The present invention is not limited to these basis weights and could beapplicable to lighter or heavier basis weight papers.

The base stock of the present invention can also be provided with apigment coating to improve smoothness of the base stock, particularlyfor base stock used for imaging. The pigment coating may include abinder present in the pigment coating composition at from about 8 toabout 30% by weight of the dry coating. The pigment to binder ratio mayrange from about 100:15 to about 100:40, more particularly from about100:20 to about 100:30.

The pigment coating composition of the present invention may includebinders and pigments typically used in pigment coatings as would beknown to those skilled in the art. Examples of pigments that may beincluded in the pigment composition include, but are not limited to,calcium carbonate pigments, clay, titanium dioxide, aluminum silicate,magnesium silicate, magnesium carbonate, zinc oxide, talc, satin white,barium sulfate, calcium silicate, zinc hydroxide, etc.

Examples of binders that may be included in the pigment compositioninclude, but are not limited to, styrene-butadiene polymers, acrylicpolymers, styrene-acrylic polymers, vinyl acetate and ethylenevinylacetate polymers.

In accordance with one aspect of the present invention, the binder usedin the coating is an acrylic latex. Examples of acrylic latexes, includebut are not limited to, acrylic esters, modified acrylic esters, acrylicester co-polymers, and modified acrylic ester co-polymers. Examples ofuseful binders include Rhoplex B-15P, Rhoplex P-554, and Rhoplex 60-A. Aparticularly preferred acrylic latex is Rhoplex B15-P available from theRohm and Haas Company. The binder is usually used in an amount of about8% to 30% by weight, more particularly from about 15% to about 25% byweight, based on the total solids content of the coating. For someapplications, the binder may be used in amounts ranging from about 20%to about 30% binder by weight. In accordance with particular embodimentsof the invention, the coating composition includes binders described incopending application Ser. No. ______ entitled “BIDER SELECTION FORCOATED PHOTOGRAPHIC BASE STOCK.”

The pigments useful in accordance with the present invention are notparticularly limited and any pigments can be used which are suitable forthe end use application of the coated paper. In accordance with certainembodiments of the invention, the pigment coating contains pigmentswhich are particularly useful in improving smoothness of the base stockas described in commonly assigned and contemporaneously filed U.S.application Ser. No. ______, entitled “PIGMENT SELECTION FOR COATEDPHOTOGRAPHIC BASE STOCK.” Examples of the pigments useful in accordancewith this aspect of the present invention include, but are not limitedto, anisotropic particles in the form of needle-shaped aragoniteprecipitated calcium carbonate, high-aspect-ratio clay, low bulk densitypigment in the form of hollow sphere polystyrene pigment andcombinations thereof. In accordance with a more specific aspect of thepresent invention, a specific pigment formulation comprising acombination of these pigments is provided. By providing a particularrange of concentrations of needle-shaped precipitated calcium carbonate,hollow sphere polystyrene pigment and high-aspect-ratio clay, theroughness of a coated photographic base paper can be minimized. Inaccordance with a particular embodiment of the invention a pigmentcoating containing from about 10 to about 14% high aspect ratio clay,from about 18 to about 22% hollow sphere polystyrene pigment and fromabout 65 to about 75% aragonite precipitated calcium carbonate based ontotal pigment weight can be used to minimize surface roughness. Thepresent invention provides levels of smoothness that are not typicallyattained using prior art techniques.

In accordance with another particularly useful embodiment of theinvention, a coated paper is provided having a pigment coatingcontaining from about 20 to about 30% of an acrylic binder, from about40 to about 80% of aragonite precipitated calcium carbonate and fromabout 15 to about 25% hollow sphere polystyrene pigment by weight basedon the dry pigment coating.

The base stock of the present invention may be used in any image formingsystem in which a smooth base sheet is required to provide a highquality image. By way of example, it may be used in conjunction withphotosensitive emulsions, water or pigment-based ink receptive layers,thermal dye-recording layers, or other specialty coatings appropriatefor a given imaging method. More particularly, a base stock produced inaccordance with the present invention can be converted into photographicproducts or used to produce photographic ink jet products.

The pigment coating as described herein may be applied to the uncoatedbase stock using any conventional coating devices, such as a gate rollcoater, a bill blade coater, an air knife coater, and the like. Thepigment coating will typically be applied to provide a coat weight offrom about 4 to about 15 lb/3300 ft², more particularly from about 8 to10 lb/3300 ft².

After being formed and dried on the paper machine to form a web, finalsmoothness of the base paper (or coated paper) is generally achieved bysubjecting the web (or coated paper) to various smoothing operations.One particularly useful method involves a densification process known ascalendering, during which a paper web is passed between nips formed bymultiple rolls stacked upon one another, creating pressure to compressthe paper and make it smoother. Generally, the compression step isaccomplished with a stack of four or more metallic rolls (U.S. Pat. No.5,060,565). In such a stack, the nip load and compression force increasein each successive nip from the top down due to the weight of the rollsand whatever additional load force is applied. In U.S. Pat. No.5,200,258, a process is described using a nip formed by two rolls ofdissimilar material (i.e. metallic and a polymeric resin covered roll)followed by a nip formed by two metallic rolls. This is a process usedfor production of standard base stocks as well. In accordance withcertain aspects of the present invention, the paper may be compressed bya succession of nips formed by either a polymeric resin covered roll anda metallic roll or by two metallic rolls. It is known in the art ofcalendering that a nip formed by a polymeric covered roll and a metallicroll will give improved fine scale smoothness to the web contacting thepolymeric covered roll. A nip formed by two metallic rolls will improvelarge to medium scale roughness resulting from paper formation-relatedroughness. In accordance with a particular embodiment of the presentinvention, the smoothing operation involves passing the paper webthrough a plurality of nips in a calender stack wherein the first nipsare formed by polymeric covered rolls adjacent to metallic rolls and thelast two nips are formed by pairs of adjacent metallic rolls. Therefore,the fine scale smoothness is improved initially with the large andmedium scale smoothness improved in the last two nips. A means isemployed to control nip pressures so calender roll weight and loadingpressure are not the only factors in determining individual nip loads.The described calendering sequence allows a high level of smoothnesswithout a blackening effect that can occur when paper is calenderedthrough multiple metallic nips.

Coated paper in accordance with the certain aspects of the presentinvention is advantageous due to the improvement in smoothness obtainedusing the described fibers and pigment coating composition. Smootherpapers provide images of higher quality in most image formingoperations. Smoothness of photobase paper is particularly important forgenerating high quality images. The surface roughness or Ra of the basestock or coated paper is a measure of relatively finely spaced surfaceirregularities on the paper. Ra represents the center line roughness ofthe base stock or finished paper. The surface roughness measurementprovides an indication of the maximum variations over the surface of thepaper. Lower Ra values indicate smoother base stock or coated paper.

In accordance with one aspect of the present invention, the base stockis subjected to a smoothing operation to provide a base stock having aroughness of from about 1.2 micron Ra to about 1.5 micron Ra. Calenderloads typically range from about 1000 pli to about 1500 pli to producebase stock having the desired smoothness. Ra represents the center lineroughness of the base stock or finished paper. Ra is preferably 3.0microns or less, more preferably 2.0 micron or less and most preferably1.5 micron or less.

In accordance with certain embodiments of the present invention, thebase stock (or coated paper) is further coated with a polymeric resinlayer on one or both sides of the base stock (or coated paper). Thepolymer film is typically applied to the base stock by an extruding orlaminating process although any method of coating the polymeric film tothe base stock to provide a smooth surface can be used. One or morecoating layers of polymer can be applied to the base stock (or coatedpaper). The polymers useful in accordance with this aspect of theinvention are not particularly limited provided the polymer is capableof being extruded, laminated or coated onto the paper base stock.

Polyolefin resins typically are used in producing a photographic supportto which a photosensitive emulsion is applied. Polyolefin resins usefulin forming the polyolefin resin layer include homopolymers of olefinssuch as low density polyethylene, high density polyethylene,polypropylene, polybutene, polypentene, copolymers of two or moreolefins and mixtures thereof. Polymers of various densities and meltindices can be used. Polyester resins or films may also be used inproducing a photographic support. The polymer resin layer may alsoinclude other additives such as pigments, amides, metal salts ofaliphatic acids, antioxidants, brighteners, ultraviolet absorbers, etc.Titanium dioxide is frequently added to the polymer resin layer toimprove sharpness and image resolution. U.S. Pat. No. 4,994,357 to Unoet al. describes various polyolefin coating compositions and the use ofthe compositions in producing photographic supports.

The polymer layer may be applied to provide a dry coat weight of fromabout 5 to about 30 lb/3300 ft², more particularly from about 15 toabout 25 lb/3300 ft². The polymer layer can be extruded as a singlelayer or co-extruded as a multi-layer.

The present invention is illustrated in more detail by the followingnon-limiting examples.

EXAMPLE 1

Base stock samples in accordance with particular embodiments of theinvention were tested using a laser based UBM surface smoothnessapparatus. Roughness of typical photographic base stock and theinvention base stock samples both measured in a range of 1.3 to 1.4micron Ra. Another surface measurement method using a stylus probe wasalso used. The stylus method separates roughness components by size intothree categories or length scales: R1, R2, and R3. R1 represents thelargest scale roughness and R3 the smallest “fine” scale roughness. Foreach roughness scale, a smaller R-value represents a smoother basepaper. Average data for three reference base stocks were: R1=36, R2=37,and R3=48. By comparison, three invention base stocks averaged R1=29,R2=36, and R3=46.

Comparison of Fiber Properties

TABLE 1 Example 1 (Standard Photo Base Stock - Comparative) Fiberlength, mm Cell Wall Population, Species Percent (unrefined) Thickness,μm Fibers per gram Eucalyptus 34 0.65 ≈4   20 × 10⁶ Maple 24 0.85 4.0512.8 × 10⁶ Aspen 23 1.05 3.20 11.9 × 10⁶ Birch 12 1.51 3.75  7.6 × 10⁶Beech 5 1.16 5.60  7.6 × 10⁶

TABLE 2 Example 2 (Invention Base Stock) Fiber length, mm Cell WallPopulation, Species Percent (unrefined) Thickness, μm Fibers per gramOak 70 1.25 5.8 6.9 × 10⁶ Yellow Poplar 10 1.95 ≈6 1.9 × 10⁶ Gum 8 1.856.32 2.2 × 10⁶ Maple 3 0.85 4.05 12.8 × 10⁶  Misc. Species 9 >1.0

Comparison of Base Stock Roughness Values

TABLE 3 Base Stock UBM Data Base Stock UBM Ra, μm Example 4 (Reference)1.32 Example 5 (Reference) 1.35 Example 6 (Invention) 1.33 Example 7(Invention) 1.38

TABLE 4 Base Stock Stylus Data Side 1 Side 2 Side 1 + side 2 avg SampleR1 R2 R3 R1 R2 R3 R1 R2 R3 Example 8 38 40 40 35 39 41 36 37 48(Reference) Example 9 41 36 47 40 36 49 Reference Example 10 28 33 49 3440 61 Reference Example 11 26 32 41 25 33 44 29 36 46 (Invention)Example 12 26 36 46 26 35 45 (Invention) Example 13 34 36 48 36 39 49(Invention)

TABLE 5 Fiber Length Analysis Results (Invention Base Stock) SampleLength-weighted Average Example 14 (Invention) 0.93 mm Example 15(Invention) 0.98 mm Example 16 (Invention) 0.93 mm Example 17(Invention) 0.90 mm

TABLE 6 Fiber Coarseness Data Coarseness Length-weighted (Length/ SampleAverage Mean Width Width) Example 18 (Reference) 0.73 mm 0.0350 mm 21Example 19 (Invention) 0.98 mm 0.0190 mm 51 Example 20 (Invention) 0.93mm 0.0193 mm 48

Having described various aspects and embodiments of the invention andseveral advantages thereof, it will be recognized by those of ordinaryskills that the invention is susceptible to various modifications,substitutions and revisions within the spirit and scope of the appendedclaims.

1. A base stock comprising fibers wherein the fibers have a fiber lengthweighted average of greater than about 0.9 mm and wherein the base stockhas a roughness of less than about 2.0 micron Ra.
 2. The base stock inaccordance with claim 1 wherein the base stock has a roughness of lessthan about 1.5 micron Ra.
 3. The base stock in accordance with claim 2wherein the base stock has a roughness of from about 1.2 micron Ra toabout 1.5 micron Ra.
 4. The base stock in accordance with claim 1wherein the base stock comprises at least 50% non-standard fibers basedon the total fiber content.
 5. The base stock in accordance with claim 1wherein the base stock comprises at least 50% fibers having a populationof less than about 10×10⁶ fibers/gram.
 6. The base stock in accordancewith claim 1 wherein the base stock is substantially free of fillerpigments.
 7. A method for producing a base stock for use in forming arecording material comprising the steps of: providing a fiber slurrycomprising fibers having a length weighted average fiber length aboveabout 1 mm, forming a web of the fibers; and subjecting the web to asmoothing operation to provide a base stock having a roughness of lessthan about 2.0 micron Ra.
 8. The method of claim 7 wherein the basestock has a roughness of less than about 1.5 micron Ra.
 9. The method ofclaim 8 wherein the base stock has a roughness of from about 1.2 micronRa to about 1.5 micron Ra.
 10. The method of claim 7 further comprising:refining the fibers in the fiber slurry, wherein after the refinementtreatment, the fibers have a length-weighted average fiber length ofabove about 0.9 mm.
 11. The method of claim 10 wherein the fiber slurryis substantially free of filler pigments and the resulting base stock issubstantially free of filler pigments.
 12. The method of claim 7 furthercomprising: coating the base stock on at least one side thereof with apigment coating composition.
 13. The method of claim 12 wherein saidpigment coating composition comprises aragonite precipitated calciumcarbonate, hollow sphere pigment and a binder.
 14. The method of claim13 wherein the binder comprises an acrylic binder selected from thegroup consisting of acrylic esters, modified acrylic esters, acrylicester co-polymers, modified acrylic ester co-polymers and mixturesthereof.
 15. The method of claim 14 wherein said pigment coatingcomposition comprises from about 20 to about 30% acrylic binder, fromabout 15 to about 25% hollow sphere pigment and from about 40 to about80% aragonite precipitated calcium carbonate based on dry weight of thepigment coating composition.
 16. A support material for an image formingsystem comprising: a base paper comprising fibers wherein the fibershave a fiber length weighted average of greater than about 0.9 mm andwherein the base stock has a roughness of less than about 2.0 micronRa.; and an image forming or image receptive coating layer on at leastone side of the paper wherein the image forming or image receptivecoating is selected from the group consisting of a photosensitiveemulsion, an ink jet receptive coating, a thermal dye recording layerand a pigment based ink receptive layer.
 17. The support material inaccordance with claim 16 wherein the support material further comprisesa pigment coating comprising a pigment and a binder on at least one sideof the paper thereby forming a pigment coated paper.
 18. The supportmaterial in accordance with claim 17 wherein the support materialfurther comprises a polymeric coating layer disposed between the pigmentcoating on the coated paper and the image forming or image receptivecoating layer on one or both sides of the support material.
 19. Thesupport material in accordance with claim 18 wherein the polymericcoating layer comprises a polyolefin or polyester coating layer.
 20. Thesupport material in accordance with claim 18 wherein the pigment coatingcoat weight is from about 4 to about 15 lb/3300 ft².
 21. The supportmaterial in accordance with claim 20 wherein the pigment coatingcomprises from about 40 to about 80% aragonite precipitated calciumcarbonate and from about 15 to 25% hollow sphere pigment by dry weightbased on total pigment coating.
 22. The support material in accordancewith claim 21 wherein the pigment coating further comprises from about20 to about 30% of an acrylic binder based on total pigment coating. 23.The support material in accordance with claim 20 wherein the pigmentcoating further comprises a binder present in the pigment coatingcomposition at from about 8 to about 30% by weight of the dry pigmentcoating.
 24. The support material in accordance with claim 21 whereinthe pigment coating is substantially free of clay.
 25. The supportmaterial in accordance with claim 18 wherein the base stock has aroughness of less than about 1.5 micron Ra.
 26. The support material inaccordance with claim 25 wherein the base stock has a roughness of fromabout 1.2 micron Ra to about 1.5 micron Ra.
 27. The support material inaccordance with claim 18 wherein the base stock comprises at least 50%non-standard fibers based on the total fiber content.
 28. The supportmaterial in accordance with claim 18 wherein the base stock comprises atleast 50% fibers having a population of less than about 10×10⁶fibers/gram.